British police have charged the UK director of the campaign group CAGE after his arrest at London’s Heathrow airport in November last year.

Muhammad Rabbani, 36, faces three months in prison and a fine of $3,200 for alleged "wilful obstruction and frustration of a search".

In a statement, CAGE said Rabbani was formally informed of the charges at Bethnal Green police station in east London on Wednesday.

It alleges Rabbani was asked to hand over passwords to devices he was carrying at the time of his arrest.

"Rabbani was unable to hand over the passwords to his devices as he was carrying crucial evidence taken from a torture survivor and did not have permission from the client to share the information," the statement by CAGE said.

"Rabbani has taken a principled stance to protect the right to privacy in an ongoing case of torture that implicates high ranking officials."

A statement by the Metropolitan Police, which covers the London area, confirmed that Rabbani was charged on Wednesday.

Stop and search

Rabbani was held at the airport under Schedule 7 powers that allows authorities at ports of entry to stop and search individuals without grounds for suspicion.

Anything carried by a person when stopped, such as electronic devices and data storage drives, can be searched and seized by the authorities if they deem it necessary.

Failure to comply with requests made by officers carrying out a search can result in criminal charges under the British Terrorism Act.

Rabbani said he was justified in his response to the request to handover the passwords.

"I do believe I am doing what any reasonable person would do under the circumstances in order to protect the privacy of a client."

CAGE, which was founded in 2003, is an NGO that advocates for individuals affected by British terror legislation both within the country and abroad.

Rabbani is currently on bail and due to appear before magistrates on June 20.